The conventional seat belt restraint system includes a shoulder portion and a lap portion. One end of the shoulder portion is commonly attached to the frame of the vehicle at a location adjacent the occupant's shoulder. By attaching the shoulder belt to the vehicle body, the vehicle body, rather than the vehicle seat, absorbs a relatively significant portion of the loads to which the occupant is exposed during a sudden deceleration of the vehicle.
In the United States, seats and seat belt assemblies must comply with the Federal Motor Vehicle Safety Standards (FMVSS). These standards have been developed to help minimize the possibility of the failure of seat and restraint designs by the forces acting on them as a result of a sudden deceleration or vehicle impact. For example, FMVSS 571.207 and 571.210 (37 C.F.R. §§571.207 & 571.210 (2008)) currently require a seat and seat belt assembly for many vehicles to withstand forces in excess of 3,000 pounds applied to the shoulder belt and lap belt portions of the seat belt.
Other countries impose their own regulations. More specifically, European countries also have safety requirements for seat and restraint designs in the event of a crash or sudden deceleration. For example, certain regulations permit only a limited amount of deformation of the D-ring of a seat belt assembly under load testing.
More recently, design efforts have been focused on attaching the upper end of the shoulder belt to the frame of the seat, instead of to the frame of the vehicle. In other words, it has become desirable to design a seat belt assembly that is integrated with the seat. An integrated seat belt assembly is generally more comfortable to the occupant and facilitates the installation of the seat and the accompanying belts within a vehicle. The shoulder belt tends to chafe the neck of the occupant less than do shoulder belts that are attached to the frame of the vehicle, due to such factors as the height of the occupant, the unevenness of the road, or whether the individual desires to recline in the seat. These considerations make wearing of a seat belt attached to the vehicle body uncomfortable.
Where the seat belt is integrated with the seat frame, however, the seat frame must include structural mechanisms to protect an occupant in the event of a collision or sudden deceleration. In this circumstance, the seat frame will experience significant forces exerted by the combination of the occupant and seat belt that would otherwise be experienced by the vehicle frame. Accordingly, in order to improve safety, and in order to comply with governmental standards and loading tests, the frame of the seat must have a much stronger design when the shoulder belt is attached to the seat frame than when it is attached to the vehicle body. Previous efforts to render the seat frame stronger have resulted in designs that are too bulky, heavy, or costly to be practical from a manufacturing standpoint. Further, previous efforts have focused on making the seat itself stronger, rather than the seat base assembly that supports the seat.
It is also desirable to include a tilt mechanism that allows the seat frame to be adjusted to a desired angle of inclination of the occupant. This tilt mechanism must allow adjustment through a predetermined angular range of rotation but must be prevented from further pivoting rotation by a stop. The tilt mechanism and the stop must be coordinated to allow the occupant to adjust the seat frame through a predetermined range without interference from the stop but to prevent further tilting motion once a predetermined limit is reached.
Thus, there is a need for a lightweight vehicle seating system, including seat base assembly, which allows a seat belt restraint assembly to be integrated with the vehicle seating system. Further, there is a need for a vehicle seat and integrated seat belt system that prevents the seat from failing in the event of a collision or sudden deceleration and that complies with national safety requirements. In addition, there is a need for a tilt mechanism that cooperates with the pivot stop to allow a predetermined range of angular rotation of the seat frame without interference but that limits further movement beyond a predetermined position. The tilt mechanism should have a relatively simple design, relatively low cost, and improved reliability.